Centrifugal impeller for a compressor

ABSTRACT

A centrifugal impeller for a compressor, through which a fluid is to pass. The impeller includes blades each having a leading edge and a trailing edge, the rotation of the impeller sucking fluid in through the front of the impeller, the fluid leaving the impeller via its outer periphery, the trailing edges of the blades being such that in a radial section plane intersecting the trailing edges of the blades, they are curved in the direction opposite to the direction of rotation of the impeller, and the trailing edge portions of the blades are redirected in the direction of rotation of the impeller to form respective end fins serving to deflect the flow of the fluid by redirecting it radially.

The invention relates to a centrifugal impeller through which a fluid, in particular a gas, can pass. The impeller is intended particularly for a turbomachine compressor. The impeller may be fitted to any type of turbomachine for stationary or aviation use, and in particular to a helicopter turbine engine.

More particularly, the invention relates to a centrifugal impeller of the type presenting an axis of rotation, a front portion of small section, and a rear portion of large section, the impeller having blades each having a leading edge and a trailing edge. The rotation of the impeller sucks fluid in through the front of the impeller, the axial speed of the fluid passing through the impeller being transformed progressively into radial speed, the fluid leaving the impeller via its outer periphery at the trailing edges of the blades. Said blades are such that in a radial section plane intersecting the trailing edges of said blades, they are curved in the direction opposite to the direction of rotation of the impeller.

In the present application, the terms “upstream” and “downstream” are defined relative to the normal direction of fluid flow through the impeller.

Furthermore, the axis of rotation of the impeller is often referred to more simply as the “impeller axis”. The axial direction corresponds to the direction of the impeller axis, and a radial direction is a direction perpendicular to said axis and intersecting said axis. Similarly, an axial plane is a plane containing the axis of the impeller and a radial plane is a plane perpendicular to said axis. The adverbs “axially” and “radially” refer respectively to the axial direction and to the radial direction.

Unless specified to the contrary, the adjectives “inner” and “outer” are used relative to a radial direction, the inner portion (i.e. the radially inner portion) of an element being closer to the axis of the impeller than the outer portion (i.e. the radially outer portion) of the same element.

Finally, unless specified to the contrary, the adjectives “front” and “rear” are used with reference to the axial direction, the fluid entering via the front of the impeller.

A compressor of an aviation turbomachine (e.g. of a helicopter turbine engine) that is of the centrifugal type or of the mixed axial-and-centrifugal type includes one or more compression stages with a centrifugal impeller of the above-specified type (also referred to as a centrifugal wheel or rotor), a casing surrounds the blades of the impeller on the outside, and one or more diffusers are situated downstream from the impeller. A fluid that is a gas, generally air, passes through such a compressor.

In the impeller, the absolute speed of the gas increases as a result of centrifugal acceleration, and the pressure of the gas increases as a result of the diverging section of the channels defined between the blades of the impeller. Thus, the gas leaves the downstream ends of the blades, i.e. their trailing edges, at very high speed.

A known example of a centrifugal impeller for a compressor is disclosed in U.S. Pat. No. 3,973,872.

An object of the invention is to improve the performance (i.e. total pressure ratio and isentropic efficiency) of an impeller of the above-specified type, for given geometrical size and corrected flow rate.

This object is achieved by an impeller wherein, in said radial section plane intersecting the trailing edge of the impeller blades, the trailing edge portion of the blades (i.e. the portion situated at the outer end of the rear portion of the blades) is redirected in the direction of rotation of the impeller so as to form respective end fins enabling the flow of fluid to be deflected by radially redirecting this flow.

In general, such deflection of the fluid flow enables the total pressure ratio to be increased without reducing the isentropic efficiency of the impeller.

Furthermore, by obtaining better control over such deflection, it is possible to increase the total pressure ratio without raising temperature. Thus, the increase in the total pressure ratio also gives rise to a greater or lesser increase in the isentropic efficiency of the impeller.

To summarize, the end fins serve to improve the performance of the impeller.

Such a centrifugal impeller for a compressor may have blades of two types: so-called “main” blades and so-called “intermediate” blades. The optional intermediate blades are interposed between the main blades and they differ therefrom in that they are axially shorter: they present shorter front portions, with the leading edges of the intermediate blades being set back (i.e. rearwards) relative to the leading edges of the main blades.

In an embodiment, the impeller has main blades only (i.e. no intermediate blades), and the main blades present end fins of the above-specified type.

In another embodiment, the impeller has main blades and intermediate blades. Under such circumstances, either the main blades are the only blades to have end fins of the above-specified type, or the intermediate blades are the only blades to have end fins of the above-mentioned type, or both the main blades and the intermediate blades present end fins of the above-specified type.

In an embodiment, in said radial section plane intersecting the trailing edges of the blades of the impeller, said end fin co-operates with the blade portions situated immediately upstream therefrom to form an obtuse angle that is greater than or equal to 155°, and that is strictly less than 180°.

In an embodiment, when the main blades of the impeller present end fins, the end fins extend from the trailing edges of the main blades of the impeller over a length that, when measured along the (curvilinear) outer edges of the main blades, represents less than 15% of the total length of said outer edges, and in particular more than 2% and less than 10% of the total length of said outer edges.

In an embodiment, when the intermediate blades of the impeller present end fins, said end fins extend from the trailing edges of the intermediate blades over a length that, when measured along the outer edges of the intermediate blades, represents less than 15% of the total length of said outer edges, and in particular more than 2% and less than 10% of the total length of said outer edges.

The above-specified ranges for angle value and for fin length serve singly or in combination to further improve the performance of the impeller.

The invention also pertains to a compressor including a centrifugal impeller of the invention. It may be a compressor of the centrifugal type, i.e. a compressor having at least one compression stage fitted with a centrifugal impeller, or a compressor of the mixed axial-and-centrifugal type, i.e. a compressor having at least one compression stage fitted with an axial impeller and at least one compression stage fitted with a centrifugal impeller.

The invention also pertains to a turbomachine, and more particularly a helicopter turbine engine including a compressor of the invention.

The invention and its advantages can be better understood on reading the following detailed description of an embodiment of the invention given by way of non-limiting illustration. The description refers to the accompanying figures.

FIG. 1 is a diagrammatic and fragmentary axial section view of a helicopter turbine engine with a compressor that includes a centrifugal impeller of the invention (the centrifugal impeller and the turbines of the engine being shown not in section, but rather in side view).

FIG. 2 is a diagram of the centrifugal impeller of FIG. 1 isolated from the remainder of the engine.

FIG. 3 is a diagrammatic and fragmentary perspective view showing the rear portions of two blades of the FIG. 1 centrifugal impeller.

FIG. 4 is a diagrammatic and fragmentary view of the rear portion of one of the blades of FIG. 3, shown in section in a radial section plane intersecting the trailing edge of the blade, this section plane IV-IV being identified in FIG. 2.

The example helicopter turbine engine 10 shown in FIG. 1 comprises a compressor 16 of the centrifugal type having a single compression stage. The compressor 16 comprises a centrifugal impeller 18 of the invention and a casing 15 surrounding the outside of the blades 24, 25 of the impeller 18. A diffuser 19 is situated downstream from the impeller 18.

The engine 10 presents an air inlet 12, the air passing via said inlet 12 to reach the compressor 16. The rotation of the impeller 18 about its axis of rotation A sucks in air via the front of the impeller and the axial speed of the fluid that passes thorough the impeller 18 becomes transformed progressively into radial speed, with the fluid leaving the impeller 18 via its outer periphery. The air penetrates into the impeller 18 in a direction that is substantially parallel to the axis of rotation A of the impeller, as represented in the section of FIG. 1 by arrows F1, and it leaves the impeller 18 in a direction that is substantially perpendicular to the axis A, as represented by arrows F2.

The air leaving the impeller 18 passes through the diffuser 19 before reaching the combustion chamber 20. The combustion gas leaving the combustion chamber 20 drives a high-pressure turbine 22 and a low-pressure turbine 23.

The impeller 18 is mounted on a shaft 21 that is driven in rotation by the high-pressure turbine 22.

With reference to FIG. 2, the impeller 18 presents a front portion of small section and a rear portion of large section. The impeller 18 has a plurality of main blades 24 extending axially from the front face 18A of the impeller to a radial plate 17 situated at the rear of the impeller 18, and radially from the hub of the impeller to the outer periphery of the impeller. Each of the main blades 24 presents a leading edge 24A situated at the front end of the impeller 18 and a trailing edge 24F situated at the outer periphery of the impeller 18, immediately in front of the radial plate 17.

The impeller 18 also includes intermediate blades 25 that are interposed between the main blades 24 and that differ from them in that they are axially shorter: the leading edges 25A of these blades 25 are set back (i.e. rearwards) relative to the leading edges 24A of the main blades 24. In contrast, the trailing edges 25F of the intermediate blades 25 are situated at the same radial distance from the axis A as the trailing edges 24F of the blades 24.

FIG. 3 is a perspective view showing in detail the rear portion of a main blade 24 and of an intermediate blade 25 of the impeller 18.

In a radial section plane (i.e. a plane perpendicular to the axis A), intersecting the trailing edges 24F and 25F of the blades 24 and 25 of the impeller 18, such as the plane IV-IV of FIG. 2, the blades 24 and 25 are curved in the direction opposite to the direction of rotation of the impeller, the direction of rotation of the impeller 18 being symbolized by arrow R in FIGS. 3 and 4.

In this same radial section plane, the portions of the trailing edges of said blades 24 and 25 are redirected in the direction of rotation of the impeller in such a manner that they form end fins 26, 27 serving to deflect the flow of air by redirecting it radially.

In this radial section plane, the end fin 26, 27 co-operates with the portion of the blade 24, 25 situated immediately upstream from said fin 26, 27 to form an obtuse angle T that is greater than or equal to 155° and that is strictly less than 180°. This angle T is shown in FIG. 4 which is a section view of the main blade 24 in the radial section plane IV-IV of FIG. 2.

In the example shown, both the main blades 24 and the intermediate blades 25 present end fins 26, 27. In other embodiments that are not shown, only the main blades 24 or only the intermediate blades 25 present such end fins.

In an embodiment, when the end fins 26 are present on the main blades 24, the length (in curvilinear abscissa) of each end fin 26 measured along the curvilinear outer edge 24E of said blade 24 represents no more than 15% of the total length of said outer edge 24E. For example, the length of the end fin represents at least 2% and no more than 10% of the total length of the outer edge 24E.

In an embodiment, when the end fins 27 are present on the intermediate blade 25, the length (in curvilinear abscissa) of each end fin 27 as measured along the curvilinear outer edge 25E of said blade 25 represents no more than 15% of the total length of said outer edge 25E. In particular, the length of the end fin represents at least 2% and no more than 10% of the total length of the outer edge 25E. 

1-9. (canceled)
 10. A centrifugal impeller for a compressor through which a fluid can pass, the impeller presenting an axis of rotation, a front portion of small section, and a rear portion of large section, the impeller comprising: blades each having a leading edge and a trailing edge, rotation of the impeller sucking fluid in through the front of the impeller, an axial speed of the fluid passing through the impeller being transformed progressively into radial speed, the fluid leaving the impeller at its outer periphery, at the trailing edges of the blades, wherein in a radial section plane intersecting the trailing edges of the blades, the blades are curved in the direction opposite to the direction of rotation of the impeller, wherein, in the radial section plane, a trailing edge portion of the blades is redirected in the direction of rotation of the impeller in such a manner that it forms an end fin such that the flow of fluid is deflected by being radially redirected, and wherein the end fin extends from the trailing edge of the blades over a length that, measured along the outer edge of the blades, represents more than 2% and less than 10% of the total length of the outer edge.
 11. The centrifugal impeller of claim 10, wherein, in the radial section plane, the end fin forms an obtuse angle that is greater than or equal to 155° and strictly less than 180°, with the blade portion situated immediately upstream from the end fin.
 12. The centrifugal impeller of claim 10, the impeller having main blades and intermediate blades situated between the main blades and axially shorter than the main blades, wherein the main blades and/or the intermediate blades present the end fins.
 13. The centrifugal impeller of claim 12, wherein the main blades present the end fins.
 14. The centrifugal impeller of claim 12, wherein the intermediate blades present the end fins.
 15. A compressor comprising a centrifugal impeller according to claim
 10. 16. A turbomachine comprising a compressor according to claim
 15. 